S-band doppler weather radar

Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.).

What is Doppler Principle?

When the source for signals and the observer are in relative motion, there is change in frequency (wavelength) observed by the observer. In case the source and observer are moving closer, frequency increases and vice versa.

Doppler Radars compares the frequency of transmitted and received signals and compute the difference in frequency. The (positive or negative) Change in frequency is directly proportional to the velocity of the target towards or away from the radar. Thus target velocity is calculated from the change in frequency observed by the Doppler radars.

About Doppler Weather Radar

The Doppler Weather Radar (DWR) provides advance information, enhancing the lead-time so essential for saving lives and property, in the event of natural disaster associated with severe weather. Though the conventional radars are able to track and predict cyclones, the DWR provides detailed information on storm’s internal wind flow and structure. The severity of the weather systems can thus be quantitatively estimated more accurately than ever before and more precise advance warnings can be generated for saving human lives and property. The polarimetric capability of the Radar will significantly improve the accuracy of rainfall estimation leading to accurate and timely flash flood warnings.

A state-of-the-art, indigenous doppler weather radar, capable of predicting with increased accuracy weather events such as cyclone occurring in 500-km radius from Kochi has been established.

Practice question:

1) Which of the following statements related to different weather radar bands is/are correct?1. X band radars are more sensitive and can detect smaller particles than S-band radars.2. C band radars also do not require as much power as S band radar.3. S band works at frequency of 2-4 GHz thus are not easily attenuated.

Select the correct answer using the codes given below:

a) 1 and 2

b) 2 and 3

c) 1 and 3

d) All

Ans: dExp: S band radars operate on a wavelength of 8-15 cm and a frequency of 2-4 GHz. Because of the wavelength and frequency, S band radars are not easily attenuated. This makes them useful for near and far range weather observation. The size of the Antenna is 8.5 meters and it requires a large motor to power it. X band radars operate on a wavelength of 2.5-4 cm and a frequency of 8-12 GHz. Because of the smaller wavelength, the X band radar is more sensitive and can detect smaller particles. These radars are used for studies on cloud development because they can detect the tiny water particles and also used to detect light precipitation such as snow. X band radars also attenuate very easily, so they are used for only very short range weather observation. Also, due to the small size of the radar, it can therefore be portable like the Doppler on Wheels.C band radars operate on a wavelength of 4-8 cm and a frequency of 4-8 GHz. Because of the wavelength and frequency, the dish size does not need to be very large. The signal is more easily attenuated, so this type of radar is best used for short range weather observation. The frequency allows C band radars to create a narrow beam width using a smaller dish. C band radars also do not require as much power as S band radar